Heat sink and information processor using it

ABSTRACT

The present invention relates to a heat sink. It is an object of the present invention to provide a heat sink at a low manufacturing cost, the life of the motor of which is long so that the reliability of the heat sink can be enhanced and, further, a sufficiently high cooling performance can be obtained and the designing of the heat sink can be easily performed. The heat sink includes: a bottom surface coming into contact with a heating element; a side on which a plurality of ventilation holes are formed; and an upper surface into which a cooling fan composed of blades and a motor is embedded and fixed.

This application is a Division of of prior application Ser. No.09/001,464, filed Dec. 31, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink. More particularly, thepresent invention relates to a heat sink used for cooling an integratedcircuit package, which generates heat, such as a microprocessor unit(MPU) incorporated into electronic equipment.

2. Description of the Related Art

Recently, concerning the integrated circuits used for a personalcomputer, especially concerning the MPU, the degree of integration isenhanced so as to enhance the function of the integrated circuit andincrease the processing speed. Therefore, the quantity of heat generatedin the integrated circuit has been increased. Accordingly, the inside ofthe casing of a personal computer is forcibly cooled by a cooling fan,and the MPU is located at a position where the cool air of the coolingfan flows, and a heat sink provided with a large number of fins is fixedto the MPU so that the MPU can be forcibly air-cooled. However, an MPUof a higher performance is now required for a personal computer. An MPUof a higher performance generates a quantity of heat larger than thatgenerated by other electronic parts. For this reason, there is used aheat sink into which a cooling fan is incorporated so that an MPU, whichgenerates a large quantity of heat, can be locally cooled by means offorcible air cooling. Such a heat sink into which a cooling fan isincorporated as a local cooling means is used to replace a conventionalheat sink into which a cooling fan is not incorporated. Accordingly,there is proposed a heat sink of small size in which the cooling fan ora portion of the cooling fan is incorporated inside the cooling fins.

FIGS. 15A-C are views showing a heat sink described in JapaneseUnexamined Patent Publication No. 62-49700 which is used as a localcooling means. FIG. 15A is a plan view which is taken from the uppersurface side, FIG. 15B is a cross-sectional view taken at the one-dottedchain line ABCD shown in FIG. 15A, and FIG. 15C is a plan view taken inthe direction of arrow Z in FIG. 15B. As shown in FIGS. 15A and 15B,this heat sink is composed in such a manner that a motor 2 a, which is adrive section for blades 2 b, is attached to the main body 1 of the heatsink, and fins 1 a are perpendicularly arranged so that they surroundthe blades 2 b. As shown in FIGS. 15B and 15C, the main body 1 of theheat sink is fixed to a heating element 3 such as a power transistor.Heat generated in the heating element is conducted to a bottom portionof the main body of the heat sink and further conducted to the fins 1 a.When the motor 2 a is driven, the blades 2 b are rotated, so thatcooling air is sucked from an upper portion of the cooling fan 2. Thecooling air to which a centrifugal force is given by the rotation of theblades 2 b cools the upper portions of the fins 1 a, and the cooling airblown out downward by the blades 2 b cools lower portions of the fins 1a. In this way, the cooling air which has been sucked from the upperportion passes through the fins 1 a is discharged into the periphery ofthe heat sink. Therefore, the main body 1 of the heat sink can be cooledand further the heating element 3 can be cooled.

FIG. 16 is a view showing the heat sink described in Japanese UnexaminedPatent Publication (PCT route) No. 8-502804. In the overall periphery ofthe main body 1 of the heat sink, there are provided a plurality ofperpendicular fins 1 a, and the cooling fan 2 is supported by the mainbody 1 of the heat sink. When the motor is arranged inside the blades 2b, the height of the cooling fan 2 in the axial direction is reduced,and when a portion of the cooling fan 2 intrudes into the main body ofthe heat sink, the thickness of the fan body 5 is reduced. When thecooling fan 2 is driven, the blades 2 b are rotated, so that a coolingair can be sucked from the upper portion. The thus sucked cooling aircools the bottom portion of the main body 1 of the heat sink and passesthrough among the fins 1 a. Therefore, the cooling air absorbs the heatwhich has been conducted from the main body 1 of the heat sink to thefins 1 a, and the absorbed heat is dissipated to the periphery of theheat sink. When this heat sink is fixed to a heating element such as anMPU, the heating element can be locally cooled.

FIG. 17A and 17B are views showing the heat sink described in JapaneseUnexamined Patent Publication No. 6-268125. FIG. 17A is a plan viewwhich is taken from the upper surface. FIG. 17B is a cross-sectionalview taken on line B—B in FIG. 17A. The motor 2 a of the cooling fan 2is fixed to the bottom portion of the main body 1 of the heat sink, andcooling fins 1 a are perpendicularly arranged in such a manner that theysurround the cooling fan 2. The bottom portion of the main body 1 of thethus composed heat sink is fixed to a heating element 3 such as an MPU.When the motor 2 a is driven, the blades 2 b are rotated, so that acooling air can be sucked from the upper portion. The sucked cooling airpasses through among the fins 1 a and discharges into the periphery ofthe heat sink. When the fins 1 a are cooled, the heating element 3 canbe cooled via the main body 1 of the heat sink.

In the heat sinks shown in FIGS. 15A-C and 17A and 17B, the motor 2 awhich drives the cooling fan 2 is directly fixed to the bottom portionof the main body 1 of the heat sink. In the driving section of thecooling fan 2, ball bearings or sleeve bearings are used, and lubricantsuch as grease or oil is charged in the bearing. Due to the abovestructure, heat is directly transmitted to the bearing from the bottomportion of the main body 1 of the heat sink located close to the heatingelement 3. Accordingly, the temperature of the bearing is raised. Whenthe temperature of the bearing is raised, the deterioration of thegrease or oil is facilitated, and the life of the motor 2 a isshortened.

In the heat sink shown in FIG. 16, the cooling fan 2 is mounted on theupper portion. Accordingly, areas of the fins 1 a arranged on the sideare small. Therefore, in order to realize a sufficiently high coolingperformance, it is necessary to provide small fins with very smallintervals between the fins. In order to realize the small fins 1 a, themanufacturing cost is increased in the cutting process. Further, sincethe intervals between the fins 1 a are very small, blocking tends tooccur when dust gathers between the fins 1 a. Accordingly, a quantity ofcooling air is lowered, and the cooling performance is deteriorated.

In the structure of the heat sinks shown in FIGS. 15A-C and 17A and 17Bin which the fins 1 a are perpendicularly arranged on the overall bottomsurface of the main body 1 of the heat sink, analysis of the flow of thecooling air becomes complicated and also analysis of the noise becomescomplicated. Therefore, it is difficult to design the heat sink.Accordingly, it is impossible to optimize the cooling performance andreduce the noise.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a heat sink of lowmanufacturing cost and long life, the cooling performance of which issufficiently high and in which the designing of the heat sink can beeasily performed.

One aspect of the invention is to provide a heat sink comprising a boxcomposed of a bottom surface coming into contact with a heating element,a side on which ventilation holes are formed and an upper surface onwhich a cooling fan having at least blades and a motor is embedded andfixed. Due to the above structure, when the design of the hole ischanged, the performance can be easily optimized, and when the uppersurface is provided on the box and the cooling fan is fixed onto theupper surface, the area of the side of the box can be sufficientlyensured, and further the deterioration of lubricant in the motor bearingcan be prevented.

Another aspect of the invention is to provide a heat sink in which thebottom surface is larger than a heat transmitting section coming intocontact with the heating element, and ventilation holes are formed atpositions on the bottom surface different from the position of the heattransmitting section. Due to the above structure, a change in the designof the hole can be performed in a wide range. Therefore, it becomes easyto optimize the performance. Further, the cooling performance can beenhanced and the noise generated by the cooling fan can be decreased.

Another aspect of the invention is to provide a heat sink in which theventilation holes formed on the bottom surface are open under thecondition that the heat transmitting section comes into contact with theheating element. Due to the above structure, the quantity of cooling airpassing through in the holes formed on the bottom surface of the box isincreased, so that the performance of cooling the bottom surface of thebox can be enhanced. Compared with a case in which holes are formed onlyon the side, the cooling air can flow smoothly. Therefore, theoccurrence of noise can be decreased.

Another aspect of the invention is to provide a heat sink comprising: abox composed of a bottom surface coming into contact with a heatingelement, a side on which ventilation holes are formed and an uppersurface, the bottom surface having a heat transmitting section cominginto contact with the heating element and also having ventilation holes;and a cooling fan composed of blades and a motor, wherein the coolingfan is embedded in the upper surface. When the upper surface is providedas described above, it is possible to ensure a sufficiently large areaof the side which connects with the upper surface. Accordingly, thecooling performance can be enhanced. Further, it is possible tointroduce a cooling air into the holes formed on the side and the bottomsurface of the box. Therefore, the occurrence of noise can be decreasedand the cooling performance can be enhanced.

Another aspect of the invention is to provide a heat sink in which aradiating member is arranged between the cooling fan and the bottomsurface of the box, and a portion of the radiating member is fixed ontothe bottom surface. Due to the above structure, surface areas of theradiating fins are added to the surface area of the box. Therefore, thecooling performance can be enhanced.

Another aspect of the invention is to provide a heat sink in which thedimensions of the box are larger than those of the heating element andare made to coincide with the outside dimensions of a socket holding theheating element, and the center of the cooling fan is located eccentricwith respect to the center of the heating element. Due to the abovestructure, it is possible to fix the box to the socket. Even if therotational center of the cooling fan is different from the heatingcenter of the heating element, it is unnecessary to change the design ofthe holes on the side and also it is unnecessary to correct the design.Since the center of each component is different, it is possible to coola portion of high temperature at the heating center by the strongest airflow sent out from the blades of the cooling fan. Accordingly, thecooling performance can be enhanced.

Another aspect of the invention is to provide a heat sink comprising: aheat sink component having a bottom surface coming into contact with aheating element; a cooling fan having at least blades and a motor and acover for fixing the fan to the heat sink component, wherein the coveris used for setting a distance so that a distance from the bottomsurface of the cover at the end of the heat sink component to the uppersurface of the heat sink component can be smaller than a distance fromthe bottom surface of the cover immediately below the fan to the uppersurface of the heat sink component. Due to the above structure, it ispossible to minimize the deterioration of the cooling performancewithout increasing the intensity of noise.

Another aspect of the invention is to provide a heat sink comprising: aheat sink component having a bottom surface coming into contact with aheating element; a cooling fan having at least blades and a motor; and acover for fixing the fan to the heat sink component, wherein the covercan be opened and closed round a hinge arranged at one end of the coverand locked at the other end. Due to the above structure, it is possibleto conduct working on the heating element without removing the cover andthe fan. That is, when the heat sink component to which the fan isattached is fixed to the heating element, it is possible to expose ahole for fixing the heat sink component by disengaging the lock of thecover and opening and closing it. Accordingly, it can be screwed andfixed there.

Another aspect of the invention is to provide a heat sink comprising: arectangular heat sink component having a bottom surface coming intocontact with a heating element; a cooling fan having at least blades anda motor and a cover for fixing the fan to the heat sink component,wherein a heat conveyance member for diffusing heat is attached to thebase of the heat sink component. Due to the above structure, thetemperature at the end portion is not lowered, that is, the temperatureof the overall heat sink can be made uniform. Accordingly, the coolingperformance can be enhanced. The reason why the temperature of theoverall heat sink can be made uniform is described as follows. In thecase of a heat sink, the shape of which is rectangular, a quantity ofheat transmitted in the longitudinal direction is decreased.Accordingly, the radiating efficiency of the heat sink is lowered at theend portion. However, according to the invention described in the claim,a heat conveyance member is arranged from the center of high temperatureto the end in the longitudinal direction. Therefore, heat can beconveyed to the end portion of the heat sink.

Another aspect of the invention is to provide an information processorcomprising: a heat sink component having a bottom surface coming intocontact with a heating element; a cooling fan having at least blades anda motor; and a cover for fixing the fan to the heat sink component,wherein a heat conveyance member is attached to the base of the heatsink component so as to convey heat to another cooling section. Due tothe above structure, even if a quantity of heat generated by the heatingelement is increased, it is possible to incorporate the heat sink havingthe fan into the mounting space used presently. Up to this time, whenthe heat sink having the fan is incorporated into a limited mountingspace, it is impossible to increase the volume of the heat sink and thecapacity of the cooling fan in the case of an increase in the quantityof heat generated by the heating element when the processing speed israised. However, according to the invention described in the claim, theheat conveyance member is arranged in the heat sink, and the increasedheat is conveyed to another cooling unit by the heat conveyance member.

Another aspect of the invention is to provide an information processorcomprising: a heat sink component having a bottom surface coming intocontact with a heating element; a heating element; and a printed circuitboard, wherein the heat sink component and the cooling fan are fixedonto the printed circuit board by a bracket for fixing the heat sinkhaving a cooling fan utilizing a hole for fixing the cooling fan. Due tothe above structure, the hole for fixing the cooling fan is used.Therefore, while it is unnecessary to conduct an additional machining,the heat sink and the cooling fan can be attached to the printed circuitboard of the apparatus. Accordingly, the occurrence of vibration andshock can be prevented at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention will become apparentfrom the following detailed description of the preferred embodiment ofthe invention, taken in connection with the accompanying drawings.

In the drawings:

FIGS. 1A and 1B are views showing the first embodiment of the presentinvention together with an MPU, wherein FIG. 1A is a perspective viewand FIG. 1B is a cross-sectional view;

FIG. 2 is a view showing the second embodiment of the present inventiontogether with an MPU;

FIGS. 3A and 3B are views showing the third embodiment of the presentinvention together with an MPU, wherein FIG. 3A is a perspective viewand FIG. 3B is a schematic cross-sectional view;

FIGS. 4A, 4B, and 4C are views showing the fourth embodiment of thepresent invention together with an PU, wherein FIG. 4A is a schematiccross-sectional view, FIG. 4B is a schematic cross-sectional view of theconventional heat sink shown for the purpose of comparison, and FIG. 4Cis a schematic illustration for explaining the mode of operation of theembodiment;

FIGS. 5A and 5B are views showing the fifth embodiment of the presentinvention, wherein FIG. 5A is a a partially cross-sectional side viewand FIG. 5B is a perspective view showing a radiating member;

FIGS. 6A and 6B are perspective views showing another example of theradiating member of the fifth embodiment of the present invention;

FIGS. 7A and 7B are views showing the sixth embodiment of the presentinvention, wherein FIG. 7A is a view showing the embodiment togetherwith an MPU connected with a socket, and FIG. 7B is a view forexplaining the effect provided by the eccentricity of a cooling fan;

FIGS. 8A, 8B, and 8C are views showing the seventh embodiment of thepresent invention, wherein FIG. 8A is a plan view, FIG. 8B is a frontview, and FIG. 8C is a side view;

FIG. 9 is an exploded perspective view showing the seventh embodiment ofthe present invention;

FIGS. 10A, 10B, and 10C are views showing the eighth embodiment of thepresent invention, wherein FIG. 10A is a plan view, FIG. 10B is a frontview, and FIG. 10C is a side view;

FIGS. 11A, 11B, and 11C are views showing the ninth embodiment of thepresent invention, wherein FIG. 11A is a perspective view, FIG. 11B is across-sectional view, and FIG. 11C is a rear view;

FIGS. 12A and 12B are views showing the tenth embodiment of the presentinvention, wherein FIG. 12(a) is a cross-sectional view, and FIG. 12(b)is a view showing a variation of the embodiment;

FIGS. 13A and 13B are views showing the eleventh embodiment of thepresent invention, wherein FIG. 13A is a cross-sectional view, FIG. 13Bis a perspective view, and FIG. 13C is a view taken in the direction ofarrow Z in FIG. 13A;

FIGS. 14A, 14B, and 14C are views showing a bracket for fixing the heatsink of the eleventh embodiment of the present invention, wherein FIG.14A is an upper surface view, FIG. 14B is a side view, and FIG. 14C is aview taken in the direction of arrow Z in FIG. 14B;

FIGS. 15A, 15B, and 15C are views showing an example of the conventionalheat sink, wherein FIG. 15A is a plan view, FIG. 15B is across-sectional view taken on line ABCD in FIG. 15A, and FIG. 15C is aview taken in the direction of arrow Z in FIG. 15B;

FIG. 16 is an exploded perspective view showing another example of theconventional heat sink; and

FIGS. 17A and 17B are views showing still another example of theconventional heat sink, wherein FIG. 17A is a plan view, and FIG. 17B isa cross-sectional view taken on line B—B in FIG. 17A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B are views showing the first embodiment of the presentinvention together with an MPU which is a heating element. FIG. 1A is aperspective view showing a heat sink together with an MPU, and FIG. 1Bis a cross-sectional view taken on a line passing through the center ofthe heat sink shown in FIG. 1A in which the heat sink is fixed to anMPU. The heat sink of the first embodiment of the invention comprises abox 10 and a cooling fan 11 arranged in the ceiling section of the box10. The box 10 is made of good heat conducting material, and the bottomof the box 10 is formed into a heat transmitting section which comesinto contact with a heating element 12. On the side walls of the box 10,there are provided a plurality of ventilation holes 13. In the ceilingsection of the box, there is provided a cooling fan composed of blades11 b and a motor 11 a to rotate the blades 11 b. This cooling fan isfixed onto the ceiling surface of the box 10 by means of screws oradhesion.

In this connection, examples of a good heat conducting materialcomposing the box 10 are: metal such as aluminum, and plastics such asresin, the brand name of which is Amoco Xydar manufactured by Wake FieldEngineering Co., into which carbon fibers are mixed. In the case ofmetal, a method of sheet metal forming or of aluminum die casting isused. In the case of plastics, the method of injection molding is used.Shapes of the ventilation holes formed on the side wall of the box 10may be circular, triangular or polygonal. While consideration is givento air speed, heat transmission and noise, the best position and thenumber of holes are determined. According to an experiment carried outby the inventors, the best result was obtained when the total area ofthe ventilation holes 13 was approximately 15% of the total area of thesides of the box 10.

In the first embodiment of the invention composed as described above,when the blades 11 b of the cooling fan 11 are rotated by the motor 11a, air is sucked from the upper surface of the cooling fan 11. Thesucked air is discharged from the ventilation holes 13 on the side wallsas shown by the arrows in FIG. 1B. Heat generated by the heating element12 is conducted from the bottom of the box 10 to the side walls. Thenthe conducted heat is cooled by a flow of air sent from the fan 11. Airwhich has absorbed the heat is discharged outside from the ventilationholes 13. In this way, an MPU 12 can be cooled by air. In thisconnection, the direction of air flow may be reversed.

According to this first embodiment, the main body of the heat sink isformed into a box-shape. Therefore, it becomes possible to extend thewall surface of the heat sink to the ceiling surface and the sidesurface portion in which the cooling fan is arranged, that is, itbecomes possible to ensure sufficiently large fin areas. For thisreason, it is unnecessary to provide cooling fins of complicated shapes,so that the fins can be manufactured at a low cost. Since the motor ofthe cooling fan is arranged at the ceiling portion distant from an MPU,the bearing of the fan is not exposed to high temperatures. Accordingly,the deterioration of lubricant charged into the bearing can beprevented, and the reliability can be enhanced.

FIG. 2 is a view showing the second embodiment of the present inventiontogether with an MPU. The structure of the second embodiment issubstantially the same as that of the first embodiment. The differentpoints are described below. The bottom portion of the box 10 is formedlarger than the outer shape of an MPU 12 to be cooled; the heattransmitting section 15 is made smaller than the bottom surface of thebox 10; and a plurality of ventilation holes 14 are also formed in aportion of the bottom surface protruding from the MPU 12. According toan experiment done by the inventors, it was possible to provide a goodresult when the total area of the ventilation holes 14 formed on thebottom surface of the box 10 was approximately 20% of the area of thebottom surface of the box. As a result, it is preferable that the totalarea of the holes formed on the sides and the bottom surface of the box10 is approximately 15 to 20% of the total area of the sides and thebottom surface of the box 10.

Since the second embodiment of the invention is composed as describedabove, the radiating area of the box of the second embodiment is largerthan that of the first embodiment. Accordingly, the radiatingperformance of the second embodiment can be enhanced. Concerning otherpoints, the second embodiment can provide the same effect as that of thefirst embodiment.

FIGS. 3A and 3B are views showing the third embodiment of the presentinvention together with an MPU. FIG. 3A is a perspective view, and FIG.3B is a schematic cross-sectional view. The structure of the thirdembodiment is substantially the same as that of the second embodiment.One different point is that the heat transmitting section 15 of the box10 protrudes from the bottom surface of the box. This protruding portioncan be formed as follows. A plate made of a good heat conductingmaterial is machined to a predetermined size and fixed onto the bottomsurface of the box 10 by means of adhesion, soldering or calking.Alternatively, in the manufacturing process in which the box 10 isformed by means of sheet metal forming, aluminum die casting orinjection molding, this protruding portion is formed from the samematerial as that of the box.

In the third embodiment composed as described above, the heattransmitting section 15 is contacted with an MPU 12 as shown in FIG. 3B.When the heat sink is operated, air is sucked into the box from theupper surface of the cooling fan 11. The sucked air is discharged fromthe ventilation holes 13 formed on the sides of the box 10 and theventilation holes 14 formed on the bottom surface. The air dischargedfrom the ventilation holes 14 formed on the bottom surface passesthrough between the bottom surface of the box 10 and the heating element12 and discharges outside. Heat generated by the MPU is transmitted tothe box 10 via the heat transmitting section 15 and radiates into air.

According to the third embodiment, while the size of the heat sink ismaintained to be the same as that of the heat sink of the firstembodiment, the cooling area can be increased, and the coolingperformance can be enhanced. In this connection, other points are thesame as those of the first embodiment.

FIGS. 4A, 4B and 4C are views showing the fourth embodiment of thepresent invention. FIG. 4A is a schematic cross-sectional view, FIG. 4Bis a schematic cross-sectional view of the conventional heat sink shownfor the purpose of comparison, and FIG. 4C is a schematic illustrationshowing the operation of this embodiment. The structure of the fourthembodiment is substantially the same as that of the first embodiment.One different point is that ventilation holes are formed on the sides ofthe air gap portion S arranged in parallel with the cooling fan 11.

In the fourth embodiment composed as described above, as shown in FIG.4C, air flows out from the overall sides of the box. Therefore, thepressure in the box 10 can be decreased, and the air speed can beincreased. Accordingly, air can be made to flow efficiently from thecooling fan 11 to the periphery. Therefore, the cooling efficiency ofthis embodiment can be more enhanced than the conventional heat sinkshown in FIG. 4B. In this connection, other points are the same as thoseof the first embodiment.

FIGS. 5A and 5B are views showing the fifth embodiment of the presentinvention. FIG. 5A is a cross-sectional view, and FIG. 5B is aperspective view showing a radiating member. The structure of the fifthembodiment is substantially the same as that of the first embodiment.One different point is that a radiating member 16 having ventilationholes 17 is arranged on the inner surface of the bottom of the box 10.This radiating member 16 is made of a good heat conducting material suchas metal or plastic, and it is formed into a fin-shape in which a diskand a circular cone are combined as shown in FIG. 5B. In the finportion, there are provided a plurality of holes 17.

FIGS. 6A and 6B are perspective views showing another example of theradiating member of the fifth embodiment. Both FIGS. 6A and 6B showother examples of the radiating member. The radiating member may beformed into a shape shown in FIG. 6A in which the inclined fins areextended in all directions. Alternatively, the radiating member may beformed into a shape shown in FIG. 6B in which the horizontal fins areextended in the transverse direction. Alternatively, other shapes may beadopted as long as the air speed, heat transmission and noise are wellbalanced.

In the fifth embodiment composed as described above, the radiating areais increased as the radiating member 16 is provided. Accordingly, thecooling performance of the fifth embodiment is higher than that of thefirst embodiment. In this connection, the effect of the fifth embodimentis the same as that of the first embodiment.

FIGS. 7A and 7B are views showing the sixth embodiment of the presentinvention. FIG. 7A is a perspective view showing the heat sink togetherwith an MPU mounted on the socket. FIG. 7B is a view for explaining theeffect of the eccentric fan. As shown in FIG. 7A, in the desk-top typepersonal computer, there is provided a socket 18 to which the MPU 12 canbe easily attached and from which the MPU 12 can be easily detached, andwhen the heat sink is used, the terminals of the MPU 12 can be connectedto the socket 18 under pressure so as to attain a positive connection.In order to realize the above attaching and detaching function, thesocket 18 requires a redundant space in one direction of the MPU 12.Therefore, the size of the socket 18 is larger than that of the MPU 12.When this socket 18 is used, the center O₁ of the cooling fan 11 can bearranged at a position eccentric to the center O₂ of the MPU 12 by adistance W when the box 10 is formed into a size which is substantiallythe same as the size of the socket 18. Since the center of the box 10 iseccentric to the center of the MPU 12, the center of the heattransmitting section 15 is also eccentric to the center.

The mode of operation of the sixth embodiment composed as describedabove will be explained below referring to FIG. 7B. Curve A is atemperature distribution curve of the MPU 12. At the middle of thetemperature distribution curve, the temperature is the highest. In thecase of no eccentricity, the cooling fan 11 is located at point B,however, in the case of eccentricity of this embodiment, the cooling fan11 is located at point C. Therefore, in this embodiment, the strongestwind sent out from the blades 11 b of the cooling fan 11 is made to blowagainst the bottom portion of the box 10 which comes into contact withthe high temperature portion of the heating element 12. Consequently,the cooling performance can be enhanced. In this connection, othereffects provided by the sixth embodiment are the same as those of thefirst embodiment.

FIGS. 8A, 8B, and 8C and 9 are views showing the seventh embodiment ofthe present invention. FIG. 8A is a plan view, FIG. 8B is a front view,FIG. 8C is a side view, and FIG. 9 is an exploded perspective view. Theseventh embodiment is composed of a heat sink main body 20, cover 21 andcooling fan 22. The heat sink main body 20 is composed in such a mannerthat a large number of radiating fins 20 b are perpendicularly arrangedon the base 20 a. The heat sink main body 20 is made of metal, the heatconductivity of which is high, such as aluminum or aluminum alloy bymeans of extrusion or cold forging. Alternatively, the heat sink mainbody 20 is made of resin, the heat conductivity of which is high.

At the center of the cover 21, there is provided a cooling fan 22. Thereis provided a ceiling plate 21 a which is inclined in a transversedirection to the cooling fan 22. This ceiling plate 21 a is made ofresin or a metal sheet and covers the heat sink main body 20. At thefour corners of the ceiling plate 21 a, there are provided resilientengaging members 21 b. The ceiling plate 21 a is detachably mounted onthe base 20 a by the claws 21 c (shown in FIG. 8B) attached to the endsof the engaging members 21 b. The cooling fan 22 is fixed to the cover21 by means of screws. In this structure, distances are determined asfollows. Distance A from the bottom surface of the cover at the endportion of the heat sink main body to the upper surface of the heat sinkmain body is smaller than distance B from the bottom surface of thecover immediately below the fan to the upper surface of the heat sinkmain body 20. In this connection, when the length of the heat sink mainbody is approximately 100 mm, in order to maintain a good balance, it ispreferable that the distances satisfy the equation B:A=5:3.

In the seventh embodiment composed as described above, the bottomsurface of the base 20 of the heat sink main body 20 comes into closecontact with the heating element. In general, the cooling fan has acharacteristic such that the intensity of noise increases when thedistance from the suction surface of the fan to an obstacle is small. Inorder to decrease the intensity of noise, it is necessary to provide apredetermined space (air gap). On the other hand, the coolingcharacteristic of the cooling fan is deteriorated at a position distantfrom the cooling fan because the air speed is lowered at the positionwhere the radiating fans are located. Due to the foregoing, in theseventh embodiment, the distance from the cooling fan to the heat sinkis increased immediately below the fan, and the distance from thecooling fan to the heat sink is decreased at the edge. Therefore, thedeterioration of the cooling characteristic can be minimized withoutincreasing the intensity of the noise.

FIGS. 10A, 10B, and 10C are views showing the eighth embodiment of thepresent invention. FIG. 10A is a plan view, FIG. 10B is a front view,and FIG. 10C is a side view. The structure of this eighth embodiment issubstantially the same as that of the seventh embodiment describedabove. One different point is a method of connecting the heat sink mainbody 20 with the cover 21. The connecting method of this embodiment isdescribed as follows. One end of the cover 21 is connected with the heatsink main body 20 by a hinge pin 23, and the other end is fixed by aspring made of a wire.

In this embodiment composed as described above, it is not necessary toremove the cover 21 and the cooling fan 22 when work is conducted on theheating element. That is, when the heat sink of this embodiment is fixedto the heating element, the spring 24 to lock the cover 21 isdisconnected so as to open and close the cover 21. Due to the foregoing,a hole in which the heat sink main body is fixed can be exposed, andscrews are inserted and fixed into the hole. Other effects of the eighthembodiment are the same as those of the seventh embodiment.

FIGS. 11A, 11B, and 11C are views showing the ninth embodiment of thepresent invention. FIG. 11A is a perspective view, FIG. 11B is across-sectional view, and FIG. 11C is a rear view. The structure of theninth embodiment is composed of a rectangular heat sink main body 20 ofwhich the bottom surface comes into contact with the heating element, acover 21 and a cooling fan 22. The heat sink main body 20 and the cover21 are made of the same material as that of the aforementionedembodiment. As shown in FIGS. 11A and 11B, there is provided a heatconveyance member 25 composed of a heat pipe made of metal of good heatconductivity on the upper surface, bottom surface or side of the base 20a of the heat sink main body 20. As shown in FIG. 11C, the heatconveyance member 25 may be divided into two pieces.

In the embodiment composed as described above, the heat conveyancemember 25 is arranged in the high temperature section at the centertoward the end portion in the longitudinal direction. Therefore, it ispossible to prevent a decrease in the quantity of heat transmitted inthe longitudinal direction of the heat sink main body 20, that is, it ispossible to prevent a decrease in the radiating efficiency at the end ofthe heat sink main body. Due to the foregoing structure, the temperatureof the end portion is not lowered, so that the overall heat sink can beuniformly heated and the cooling performance can be enhanced.

FIGS. 12A and 12B are views showing the tenth embodiment of the presentinvention. FIG. 12A is a cross-sectional view, and FIG. 12B is a rearview showing a variation of the tenth embodiment. The structure of thisembodiment is composed of a rectangular heat sink main body 20 of whichthe bottom surface comes into contact with the heating element, a cover21, a cooling fan 22 and a heat conveyance member 24. The heat sink mainbody 20 and the cover 21 are made of the same material as that of theaforementioned embodiment. In this embodiment, the heat conveyancemember 25 is attached to another cooling section 26. Alternatively, theheat conveyance member 25 is directly attached to the casing 30 as shownin FIG. 12B. In this connection, in the view, reference numeral 27 is amother board, reference numeral 28 is a heating element, and referencenumeral 29 is a system fan.

In this embodiment composed as described above, the heat conveyancemember 25 is arranged in the heat sink, so that heat can be conveyed toanother cooling section. Accordingly, this embodiment can solve theconventional problems in which the heat sink capacity can not beincreased and the fan capacity can not be increased when the processingspeed is raised and the quantity of generated heat is increased, becausethe space to accommodate the heat sink having a fan is limited in theconventional structure. According to this embodiment, the problemscaused when a quantity of generated heat is increased can be solved byproviding a mounting space in which the present heat sink having a fanis mounted. Accordingly, this embodiment can contribute to anenhancement of the apparatus.

FIGS. 13A and 13B are views showing the eleventh embodiment of thepresent invention. FIG. 13A is a cross-sectional view, FIG. 13B is aview taken in the direction of arrow Z in FIG. 13A. The structure ofthis embodiment is composed of a heat sink main body 20 of which thebottom surface comes into contact with the heating element 27, a coolingfan 22, a heating element 28, and a printed circuit board 31. The heatsink is fixed onto the printed circuit board 31 by a bracket 32 forfixing the heat sink, wherein the bracket 32 uses a hole for fixing thecooling fan 22.

In this connection, as shown in FIGS. 14A, 14B, and 14C, the bracket 32for fixing is composed in such a manner that legs 32 c are formed atboth end portions of the bar 32 b having two holes 32 a for fixing thecooling fan 22. The reason why the interval of these two legs 32 c islonger than the length of the heat sink main body 20 is to prevent wiregathering to an MPU which is a heat generating element. When thisembodiment is applied to a case in which the center of gravity of theheating element is high and the heating element is susceptible to damageby vibration and shock, it is possible to take a countermeasure againstvibration and shock at a low cost.

According to the heat sink of the present invention, the main body ofthe heat sink is formed into a box-shape having an upper surface, andthe cooling fan is embedded in the box. Therefore, it is possible tomanufacture a heat sink, at a low cost, the cooling capacity of which ishigh and the designing of which can be easily performed. Since thecooling fan is fixed onto the upper surface, it is possible to preventthe temperature of the bearing of the cooling fan from becoming high, sothat deterioration of lubricant is prevented and the reliability can beenhanced. When the heat conveyance member is incorporated into the mainbody of the heat sink, the cooling efficiency can be enhanced, whichcontributes to an enhancement of the performance of the apparatus.

It is to be understood that the invention is by no means limited to thespecific embodiments illustrated and described herein, and that variousmodifications thereto may be made which come within the scope of thepresent invention as defined in the appended claims.

What is claimed is:
 1. A heat sink comprising: a box composed of abottom surface coming into contact with a heating element, a side onwhich ventilation holes are formed and an upper surface on which acooling fan having at least blades and a motor is embedded and fixed,wherein the bottom surface is larger than a heat transmitting sectioncoming into contact with the heating element, and ventilation holes areformed at positions on the bottom surface different from the position ofthe heat transmitting section.
 2. The heat sink according to claim 1,wherein the ventilation holes formed on the bottom surface are openunder the condition that the heat transmitting section comes intocontact with the heating element.
 3. A heat sink comprising: a boxcomposed of a bottom surface coming into contact with a heating element,a side on which ventilation holes are formed and an upper surface, thebottom surface having a heat transmitting section coming into contactwith the heating element and also having ventilation holes; and acooling fan composed of blades and a motor, wherein the cooling fan isembedded in the upper surface.
 4. The heat sink according to claim 3,wherein a radiating member is arranged between the cooling fan and thebottom surface of the box, and a portion of the radiating member isfixed onto the bottom surface.
 5. The heat sink according to claim 3,wherein the dimensions of the box are larger than those of the heatingelement and made to coincide with the outside dimensions of a socketholding the heating element, and the center of the cooling fan islocated eccentric with respect to the center of the heating element.